Mobile phones, personal digital assistants (PDAs), digital cameras, MP3 players, televisions, monitors, interior and exterior lights, and other electronic devices utilize SSL devices (e.g., white light LEDs) for illumination. However, true white light LEDs are not available because LEDs typically emit light at only one particular wavelength. For human eyes to perceive the color white, a mixture of wavelengths is needed.
One conventional technique for emulating white light with LEDs includes depositing a converter material (e.g., a phosphor) on an LED. For example, as shown in FIG. 1A, a conventional SSL device 10 includes a support 2, an LED 4 attached to the support 2, and a converter material 6 deposited on the LED 4. The LED 4 can include one or more light emitting components. For example, as shown in FIG. 1B, the LED 4 can include a silicon substrate 12, an N-type gallium nitride (GaN) material 14, an indium gallium nitride (InGaN) material 16 (and/or GaN multiple quantum wells), and a P-type GaN material 18 on one another in series. The LED 4 can also include a first contact 20 on the P-type GaN material 18 and a second contact 22 on the N-type GaN material 14. Referring to both FIGS. 1A and 1B, the LED 4 emits a blue light that stimulates the converter material 6 to emit a light (e.g., a yellow light) at a desired frequency. The combination of the emissions from the LED 4 and the converter material 6 appears white to human eyes if the wavelengths of the emissions are matched appropriately.
FIGS. 2A and 2B are cross-sectional and top plan views, respectively, of a conventional SSL device 50 having a plurality of commonly connected LEDs 4. Referring to FIG. 2A, the SSL device 50 can include a support 52, a plurality of LEDs 4 attached to the support 52, and a converter material 56 over the substrate 52 and the LEDs 4. The SSL device 50 also has a single lens 58 over the LEDs 4. Referring to FIG. 2B, the SSL device 50 can further include a plurality of electrostatic discharge devices (ESDs) 60 and an electrical circuit having a first contact 62 and a second contact 64. All of the LEDs 4 and ESDs 60 are commonly connected to the first contact 62 and the second contact 64 such that all of the LEDs 4 operate together.
One drawback of the conventional SSL device 50 is that the single, large lens 58 has a complex emission pattern and is subject to total reflection losses. The conventional SSL device 50, therefore, may not be useful for applications that require beams or other types of collimated light. Additionally, the complex emission patterns may have bright spots and dark spots that limit the utility of the SSL device 50 for applications that require uniformly diffused emissions (e.g., backlights for displays and televisions).